comparing the E60-15 to the G70-15 isn't a fair comparison/
As far as I know the only other car to use the G70-15 was a late 60's big bodied GM, I'm thinking maybe impala????
The E60-15 was used on all kinds of intermediate cars from GM and AMC - so your sales potential is much greater.

As far as an initial production run, I would lean towards less than 500 tires total. And if they don't sell my bet is it's the only run

Talk to Jim Miner and see if a group buy is possibile. He's a Goodyear store owner( aka Kelsey tire sales outlet ) AND a vintage Mopar owner